Aircraft structures have many components that have complex shapes with multiple curvatures. For example, various complex shapes are found in aircraft nacelle and pylon systems, thrust reversers and rocket thruster chambers, among others. Several methods are known to form complex shapes. For thermoplastic and thermoset polymers, multiple tools can be used in injection and compression molding operations to form complex shapes. Metal forming techniques have used casting plugs to facilitate the formation of metallic rocket thrust chambers having hour-glass configurations. These methods, however, are not readily adaptable for forming complex parts using vacuum bag composite techniques.
Vacuum bag forming is a method of composite fabrication that can be used to form complex shapes using multiple tools. In vacuum bag forming, a vacuum pulls a preform around the contours of a tool. Where multiple tools are used to form composite parts, there must be sufficient vacuum sealing between the tools. Vacuum integrity and proper tool alignment is important to achieve desired end-product form and properties. Because the vacuum pulls a preform into every contour, seam defects result if there is less than precise alignment between the tools. Mechanical fasteners such as bolts and the like have attempted to ensure alignment among multiple tools. Such systems, however, can be cumbersome, costly and inadequate to minimize seam defects. In terms of vacuum integrity, gaskets, o-rings and similar devices have been used to improve vacuum integrity between adjacent tools. These attempts often result in less than full vacuum integrity leading to possible product defects, poor resin cure and poor resin-to-matrix migration, contributing to potential product deficiencies. In response, some have attempted to use multiple vacuum barriers to ensure vacuum integrity, but such solutions increase processing complexity and cost.
A need has arisen for the ability to form multiple curvature composites, either integrally formed or formed with minimal sub-parts, where the seams are minimized, sufficient vacuum integrity is achieved and misalignment of tools is reduced. Further, there is a need for an efficient method of forming complex shapes while providing flexibility to accommodate changing design constraints.